This invention relates, in general, to emollient compositions having a specified conductivity and range of viscosity and to methods of applying such emollient compositions to a substrate. The present invention relates, more specifically, to emollient compositions in a liquid form having sufficient conductivity and viscosity to be electrostatically sprayed. Yet more specifically, this invention relates to electrostatic methods of applying conductive emollient compositions, to essentially any substrate, but particularly to the more common forms of paper tissue, e.g. bath or toilet tissue, paper towels, facial tissue and the like. The present invention is especially applicable to large scale commercial, tissue making processes for producing emollient-coated or emollient-carrying tissue.
An "emollient" is defined as an agent that softens and smooths the skin The American Heritage Dictionary (1982). Emollients, salves, cleansing agents, and the like have been applied to substrates or carriers, such as tissue paper, for subsequent application to skin to reduce skin irritation and inflamation but also to enhance cleaning. See, e.g. Dake et al. U.S. Pat. No. 4,112,167, the Dake et al. patent being incorporated by reference herein.
Emollients, especially emollients applicable to tissue substrates, generally tend to fall into at least two broad categories, i.e., mineral oil-based emollients and silicone-based emollients. Mineral oil-based emollients usually comprise long chain alcohols. See, e.g., U.S. Pat. Nos. 4,112,167, 4,481,243, and 4,513,051. Silicone-based emollients typically contain polysiloxane of various molecular weights along with other silicone-based compounds. See, e.g. U.S. Pat. Nos. 4,950,545; 5,227,242; 5,246,546; and 5,385,643.
Whether mineral oil-based or silicone-based, such emollients are conventionally applied to tissue paper or other such substrates or carriers by dipping, see e.g., U.S. Pat. No. 3,896,807, air spraying, see, e.g., U.S. Pat. Nos. 5,227,242 and 4,950,545, and printing, see, e.g., U.S. Pat. Nos. 5,389,204; 5,389,643; and 5,525,345. The teachings of the aforementioned patents, as well as the patents mentioned in the previous paragraph are incorporated by reference herein.
Conventional methods used to coat or treat tissue substrates or carriers with emollients, especially paper substrates in a tissue manufacturing processes, have one or more drawbacks. Spraying of emollients onto a substrate or carrier, is accomplished using air pressure to force the composition through an orifice in a sprayer head. This creates a dispersed stream of emollient which is directed toward a substrate surface passing beneath or beside a sprayer head, thereby coating it. Air-driven sprayer heads tend to deliver solutions in the form of unevenly sized droplets, and in an uneven spray pattern. They also tend to require overlapping spray paths or patterns in order to obtain complete substrate coverage. Thus, surfaces coated or treated with emollients delivered by conventional air spray methods tend to be unevenly coated or to be coated excessively in regions of spray overlap. Air-driven sprayers also tend to "overspray" i.e., to miss the substrate. Overspray wastes solution, can cause air pollution, and can present a safety issue to the extent slippery working surfaces are created.
Printing of emollients on substrates, is accomplished by applying an emollient to a heated transfer surface and transferring the emollient to the substrate by placing it in direct contact with the substrate. See, e.g., U.S. Pat. Nos. 5,385,643; 5,389,204 and 5,525,345. Emollients can be applied to absorbent substrates, such as tissue paper, in a very uniform fashion using traditional printing methods. However, printing requires a substantial investment in printing equipment which is generally more costly than spraying equipment. Printing equipment also tends to become clogged as fibers are transferred from tissue paper and thus requires continuous cleaning.
Other methods for applying solutions to substrates, such as tissue paper substrates, have been developed. However, the alternative methods developed so far address some of the problems of the conventional methods discussed above but introduce others. For example, one such alternative application method, disclosed in United States patent U.S. Pat. No. 3,484,275, involves moving an electrostatically charged paper web past a grounded sprayer head. Solution ejected from the sprayer head is attracted to the electrostatically charged paper web substrate and is deposited thereon. The method of the U.S. Pat. No. 3,484,275 patent does not address the uneven droplet size or uniformity of spray problems.
Accordingly, it is an object of the present invention to provide a conductive emollient composition capable of being rapidly and precisely deposited on an substrate, preferably on a tissue or paper substrate, and more preferably on a facial tissue substrate in a commercial tissue making process, using an electrostatic sprayer apparatus.
It is a further object of the present invention to provide a method for rapidly and precisely applying a conductive emollient composition to a moving tissue paper substrate using an electrostatic sprayer apparatus, with minimal overspray and spray overlap, to produce a tissue substrate uniformly coated with emollient.